Disposable diaper, fabric useful therein, and method of manufacture

ABSTRACT

A non-woven fabric is disclosed which comprises a highly waterabsorbent web of mixed long and short fibers that is throughbonded throughout its dimensions with a binder (adhesive) to retain the fibers in their assembled relationship. In the final set stage of the binder it is hydrophobic in character and hence the resulting fabric is rendered more or less water repellent. In the invention the mid-portion of the bonded fabric is treated with a wetting agent (surfactant) to minimize the water-repellent effect of the binder and to make the mid-portion of the fabric readily wettable. Marginal portions of the bonded fabric are not treated with a wetting agent, so that these portions of the fabric throughout their dimensions are more or less water repellent. By this is meant that the marginal portions of the bonded fabric are difficultly wettable as compared to the midportion of the fabric. As indicated, the binder material at the side edges of the fabric is present throughout the thickness of the fabric, and hence it is effective to prevent liquid that is wetted into the central portion of the fabric from wicking readily outwardly. The fabric of the invention has particular utility as a facing layer in a disposable diaper that includes an absorbent pad and a water repellent backing member, since it minimizes liquid leakage from the side edges of the diaper. In another embodiment, the portions of the fabric not treated with wetting agent include periodic bands across the continuous length of the fabric spaced apart so that when the continuous fabric is cut into facing fabric lengths, the end margins of the facing fabric will also be more or less water-repellent.

United States Patent [1 1 [111 3,837,343 Mesek 1*Sept. 24, 1974DISPOSABLE DIAPER, FABRIC USEFUL THEREIN, AND METHOD OF [57] ABSTRACTMANUFACTURE A non-woven fabric is disclosed which comprises a highlywater-absorbent web of mixed long and short [75] lnvemor' gigg ing MesekDowners fibers that is through-bonded throughout its dimensions with abinder (adhesive) to retain the fibers in gnee: Johnson & JOhIISOIl, Newtheir assembled relationship. In the final set stage of Brunswick, thebinder it is hydrophobic in character andhence 1 Notice: The portion ofthe term of this the resulting fabric is rendered more or less waterrepatem Subsequent to May 1 1990, pellent. In the invention themid-portion of the has been disclaimed bonded fabric is treated with awetting agent (surfactant) to minimize the water-repellent effect of theFiledi 1973 binder and to make the mid-portion of the fabric [2}] Appl345,398 readily wettable. Marginal portions of the bonded fabric are nottreated with a wetting agent, so that these Related Application Dataportions of the fabric throughout their dimensions are [63] c n i i i nof s 137,249, 7, more or less water repellent. By this is meant that the1971, Pat. No. 3,730,184. marginal portions of the bonded fabric aredifficultly wettable as compared to the mid-portion of the fabric. [52]US. Cl. 128/287, 128/284 As indicated, the binder material at the sideedges of [51] Int. Cl. A61t' 13/16 the fabric is present throughout thethickness of the [58] Field of Search 128/284, 286, 287, 290 R, fabric,and hence it is effective to prevent liquid that is 128/290 W, 296wetted into the central portion of the fabric from wicking readilyoutwardly. The fabric of the invention [56] References Cited hasparticular utility as a facing layer in a disposable UNITED STATESPATENTS diaper that includes an absorbent pad and a water re- 2 649 8588/1953 Le Bolt 128/287 Penent backing m b since it .minimizes liquid3:017:304 l/1962 Burgeni 128/290 R leakage fwm the We edges of thediaper- 3,22 ,738 12/ 1965 Ekberg et a u 128/237 In another embodiment,the portions of the fabric not 3,431,911 3/1969 Meisel, .Il. 128/287treated wetting agent include periodic bands 3:35:2 across thecontinuous length of the fabric spaced apart so that when the continuousfabric is cut into facing Jones 128/290 R fabric lengths, the endmargins of the facing fabric will Mesek 128/287 Primary Examiner-AldrichF. Medbery also be more or less water-repellent.

17 Claims, 9 Drawing Figures PAIENIEDsnu-mn SHEEIMF 3 DISPOSABLEDIAPER,'FABRIC USEFUL THEREIN, AND METHOD OF MANUFACTURE CROSS-REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTIONDisposable diapers have met with increased commercial acceptance inrecent years primarily because of their convenience, as opposed to clothdiapers, which need to be laundered once soiled. Many differentconstructions have been proposed and used, and some have met withwidespread commercial success in spite of certain inadequacies infunctional properties.

One of the most serious prior art problems has been the inability toprovide a suitable construction that would keep moisture away from thesurface of the diaper which comes into contact with the infants skin andthereby avoid skin irritation and infection. Mesek, et al., US. Pat. No.3,612,055, issued Oct. 12, 1971, discloses several diaper constructionsthat function extremely well in keeping moisture away from an infantsskin, while at the same time handling a full volume of urine.

These functions are accomplished by a multilayer diaper comprising, inorder, a fibrous facing layer which is to be brought into contact withthe infants skin, a' layer of highly porous, loosely compactedcellulosicbatt, a paper-like, densified, highly compacted cellulosic fibrous layerintegral with the loosely compacted batt and an impervious backing sheetadhered to the densified layer throughout the interface therebetween.The facing layer is of porous construction and its fibers have lesswettability for water than the fibers of the loosely compacted batt,resulting in a tendency for liquid to flow from the facing web into thebatt. The densified fibrous layer has a smaller average pore size thanthe loosely compacted batt, resulting in a tendency for liquid to flowpreferentially from the batt into the underlying densified layer ratherthan to other areas-of the batt, thus tending to restrict wetting in thebatt to an area of moderate size. Liquid flowing into the densifiedlayer tends to spread laterally because of its wicking action and liquidwhich might pass through the densified layer during discharge (when flowis rapid) is held back by the impervious backing sheet for sufficienttime to permitabsorption to take place. Liquid in excess of theabsorptive capacity of the densified layer is forced back by theimpervious layer into the dry portion of the loosely compacted batt,thus utilizing the additional absorptive capacity therein.

The facing layer in the abovedescribed diaper is comprised of a mixtureof long and short fibers that are held together by a binder having awetting agent therein which reduces thewater repellency of thefacinglayer, so that urine may readily pass therethrough and into theloosely compacted batt. The binder and wetting agent are uniformlyapplied across the width and thickness of the facing layer so that thefacing layer has uniform functioning properties. While the above type offacing layer has functioned satisfactorily in use, in certaincircumstances, particularly when the diaper becomes saturated; there hasbeen a'tendencyfor urine to wick along the facing layer and causeleakage at the edges of the diaper. It has been proposed to obviate thisproblem by spraying, or otherwise applying, a waterrepellent agent onthe edges of the facing layer in an effort to prevent urine from wickingoutwardly, but this proposal has proven to be unsatisfactory, since thewater-repellent agent does not penetrate throughout the thickness of thefabric and hence does not prevent the wicking action.

SUMMARY OF THE INVENTION The present invention provides an improvednonwoven fabric having particular utility as the facing layer in adisposable diaper of the type disclosed in the above mentionedapplication. The facing layer of the present invention is absorbent andreadily wettable in the central portion and water-repellent (difficultywettable) at at least two opposite marginal portions. The facing layermay be conveniently produced by treating the mid-portion of a web ofmixed short and long fibers with a binder and a wetting agent, andtreating marginal portions of the web with binder material only. Thebinder material is used in an amount sufficient to impart to marginalportions of the facing layer, after the binder has cured, the desireddegree of water repellency.

In the application of the binder material to the web of mixed short andlong fibers, the binder material is flowed onto the web in an amount inexcess of the minimum amount required to retain the fibers in theirassembled relationship. The binder material is drawn through the facinglayer, as by suction, so that the web is thoroughly impregnated. Asalready indicated, the binder material applied to the central portion ofthe web has incorporated therein a wetting agent, whereas that appliedto the marginal portions does not, so that a means is provided in theresulting facing layer of the invention to effectively prevent urinefrom wicking readily outwardly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view, withcertain portions broken away for clarity of illustration, of an openunfolded diaper of one embodiment of this invention;

FIG. 2 is an enlarged cross-sectional view taken generally along line 22of FIG. 1;

FIG. 3 is a perspective view on a reduced scale of the diaper of FIGS. 1and 2 in its configuration after being put on an infant;

FIG. 4 is a simplified schematic view of the production line on whichthe diaper is made;

FIG. 5 is an enlarged perspective view illustrating the binder applyingmeans utilized in the production line of F FIG. 6 is an enlargedperspective view of a modified DETAILED DESCRIPTION OF THE INVENTIONReferring to the drawings, and particularly to FIGS. 1 and 2, the diaperassembly 10, when fully opened and laid out flat, comprises a lowermostwater-impervious sheet 12 which is rectangular in shape, a highlywaterabsorbent fibrous pad, or batt 14, which is also rectangular inshape, but smaller than the impervious sheet and centrally disposedthereon, and an overlying facing layer 16 of fibrous material, which isalso rectangular in shape,-equal in dimension, and coterminous with theimpervious sheet and in contact therewith in the portions of the diaperextending peripherally beyond the absorbent pad, i.e., in the portions16b and 12b of facing layer 16 and impervious sheet 12, respectively.The batt 14 has a paper-like densified highly compacted lowermostfibrous layer 18 which is adhered to the impervious sheet by bead linesof adhesive 22 substantially throughout the interface therebetween.Portions 16b and 12b are also adhered to each other by bead lines 22.

In the preferred embodiment of the invention, moisture-impervious sheet12 is formed of polyethylene having a thickness of approximately 0.001inch. The sheet may be smooth, or may be embossed to improve its drapeand feel. Other suitable flexible moistureimpervious sheets may be usedin accordance with the invention, such as, for example, polyethyleneterephthalate sheets having a thickness of about 0.0005 inch.

In the embodiment of FIG. 9, the general structure of the diaper issimilar to the structure described above with reference to FIG. 1; andall of the elements described above find their couterparts in FIG. 9 andare designated in the latter Figure by numerals higher than those ofFIG. 1 by 100. For convenience, these elements will be referred toherein by the reference numerals they bear in FIG. 1.

In addition to the foregoing elements, there are in the facing layer ofthe diaper of FIG. 1 side edge portions 16a which are of lesserwettability than the remainder of the facing layer. The diaper of FIG. 8has similar side edge portions 116a and also has end edge portions 116dwhich are also of lesser wettability than the remainder of the facinglayer. Together, portions 116a and 116d comprise a rectangular border orpicture frame" of reduced wettability surrounding the central portion ofthe facing layer.

The relative sizes of the central portion and the edge portions in theembodiments of FIGS. 1 and 8 are matters of design dependent on a numberof factors including the overall size of the diaper and whether it isintended for a newborn infant or for a larger and more active baby.Generally, the central portion will comprise from about 50 percent toabout 90 percent of the total area of the diaper and the marginalportions will range from about inch to about 2 inches in width.

Butt 14 is formed of loosely compacted short cellulose fibers, such aswood pulp fibers, or cotton lintess, or mixtures thereof, which areprimarily held together by interfiber bonds requiring no added adhesive,as is known in the art. Briefly, this batt is a low bulk densitycoherent web of loosely compacted cellulose fibers preferably comminutedwood pulp fibers in the form of so-called fluff.

The term short fibers, as used herein, refers to fibers less than aboutA inch length, in contrast to long fibers, or textile length fiberswhich are longer than about l inch in length, and generally are betweenabout k and 2% inches in length. The former are sub stantially lesscostly than the latter. The classification of fibers by length may becarried out by the Clark Classification procedure described in the testmanual of The Technical Association of Pulp And Paper Industry(TAPPI-T233 SU64).

The paper-like densified layer 18 of batt 14 is formed by a slightmoistening of one surface of the batt followed by the application ofpressure thereto. The nature of the batt and of its densified layer andthe method of producing the same are described in US. Pat. No.3,017,304, dated Jan. 16, I962.

The composite density of batt 14, including its densified layer 18,should be above about 0.07 gm./cc., and preferably between about 0.10and 0.15 gm./cc. The foregoing density values are applicable to thediaper as produced. In storage and handling, the loft or thickness ofthe batt is increased to some extent, resulting in lowered densities.

Facing layer 16, as described in the above-mentioned Mesek et al.patent, is made up of a mixture of fibers consisting predominantly ofshort cellulosic fibers such as wood pulp fibers or cotton linters, inamounts of about percent to about 98 percent, the balance being textilelength fibers such as rayon. Short cellulosic fibers such as wood pulpfibers or cotton linters are substantially less expensive than textilelength cellulosic fibers such as cotton and rayon, and this low cost isa factor in reducing the cost of the facing layer component of thediaper of this invention.

In the facing layer, the short fibers are in uniform admixture with 2percent to about 25 percent by weight of textile length fibers, such as1.5 denier rayon fibers uniformly cut to 1% inch length. The short andlong fibers are randomly and substantially uniformly dispersed andbonded with a bonding agent such as a selfcross-linking acrylicemulsion, and as is hereinafter described in detail, the web isimpregnated with a binder fluid by flowing a solution or dispersion ofthe binder over the web. As a result, the binder is substantiallyuniformly distributed throughout the thickness of the web.

In accordance with another preferred embodiment of this invention, thefacing layer comprises a mixture of long and short fibers which variesin composition with respect to proportions of long and short fibers indifferent thickness portions of the web. Such webs and the methods offorming them are disclosed in the commonly owned copending US. Pat.application Ser. No. 108,546 of Ruffo, et al., filed Jan. 21, 1971, thedisclosure of which is hereby incorporated by reference. The preferredweb of the Ruffo, et al., application for the facing layer of thisinvention has a given overall concentration of long and short fibers, agreater concentration of long fibers at one major face (the exteriorface of the facing layer as the diaper is assembled), a greaterconcentration of short fibers at the opposite major face and a uniformtransition of fiber concentrations at different thickness portions atincreasing distances from one major face to the other.

In the diaper of the aforementioned Mesek, et al., patent the binderfluid impregnated into the facing web contains a surfactant or wettingagent to partially counteract the water repellency of the bonding agentand bring the facing layer to the desired degree of wettability.

In accordance with the present invention, it is only the central portionof the web, comprising the major portion of its area, and including allportions likely to be initially wetted when the diaper is in use. Inaccordance with the present invention, the marginal end and side and/orend edges of the facing layer are treated with a lesser amount ofwetting agent, or no wetting agent at all. By not treating the marginaledges of the facing layer with a wetting agent, these portions of theweb are less wettable and less absorbent than the mid portion of theweb, which minimizes any tendency for urine to spread outwardly in thefacing layer.

Facing layers suitable for use in this invention have fabric weights inthe range of l to 5 oz./yd and preferably I to 2 oz./yd and densitiesless than 0.15 gm./cc., generally in the range between 0.05 and 0.1gm./cc. The dry strength of the facing layer, for a fabric having aweight of about 1.5 oz./yd is at least 0.12 lbs./in., preferably 0.15lbs./in. of width in the machine direction and at least 0.08 lbs./in.,preferably 0.10 lbs./in., of width in the cross direction. The fabricshave unusually good elongation, loft, softness and drape characteristicsin comparison to prior products incorporating any substantial amount ofshort fibers.

An important aspect of this invention is the provision for selectivewettability among the above-described fibrous components of the diaperand within the components themselves, such that the moisture isselectively drawn from the facing layer into the body of the batt andthen from the body of the batt into the densified layer thereof.

The least wettable of the fibrous elements of the dia per of thisinvention is facing layer 16. However, even in the facing layer theability to be wetted by water is desired. Water repellency in thecentral portion of the facing layer is not desired since, at the desiredfiber densities in the facing layer, water repellency can prevent theliquid from penetrating into the facing layer and the absorbent layersbehind it, just as a tent fabric holds back penetration of rain water.For this reason, the central portion of the facing layer is treated witha wetting agent, such as an anionic or a non-ionic surfactant, tomoderate and reduce the water repellency which may be imparted to theshort and long fibers of the web by the bonding agent which bonds theminto an integral layer. After treatment with a wetting agent, thecentral portion of the facing layer is receptive to penetration by urinebut remains less wettable than the batt.

Water repellency, or at least reduced wettability, is desirable at themarginal edges of facing layer 16 to minimize any tendency for urine towick along the facing layer toward the marginal edges thereof. In accordance with the present invention differential wettability in the facinglayer can be accomplished by not treating the marginal edges of thefacing web with a wetting agent, so that only fibers and binder materialare present at the marginal edges, or by applying more binder to themarginal edges of the facing web than to the midportion thereof.

A useful parameter of wettability is the liquid-fiber contact angle forthe individual fibers of the layer, the contact angle approaching 90 forfibers which are difficultly wettable, exceeding 90 for fibers which arehighly water repellent and approaching zero for fibers which are highlywettable by water. The liquid-fiber contact angle may be determined frominterface high speed photographs of individual dry fibers, held in aclamp, and advanced into the wetting liquid (water) at a rate of 0.5cm./sec. by techniques known in the art.

In any particular facing layer, the liquid-fiber contact angle forindividual fibers may vary considerably because of unevenness ofdistribution of the waterrepellent bonding agent andunevenness ofdistribution of wetting agent and/or surfactant. Nevertheless, aliquid-fiber contact angle between about 30 and about 60 for most (overpercent) of the individual fibers in a random selection providessuitable wettability in the central portion of the facing layer, and aliquidfiber contact angle between about 40 and about is preferable. Aliquid-fiber contact approaching and preferably above 90 gives themarginal side edges of the facing layer an adequate degree of waterrepellency.

The body of batt 14 is substantially more wettable than the facing layerand tends to draw liquid away from the facing layer. The individualfibers of the batt are extremely wettable, generally having liquid-fibercontact angles below about 15 and approaching zero in the optimumembodiment. The wickability, or preferential absorptivity of the body ofthe batt for water is limited, however, by its low density which resultsin a large effective capillary radius for the capillaries betweenadjacent fibers.

The pressure causing a liquid to enter a cylindrical capillary isexpressed by the equation:

P Zycos O/r where P is the capillary pressure, I

'y is the surface tension of the liquid,

0 is the liquid-fiber contact angle, and

r is the capillary radius.

With a given liquid, the pressure (capillary force) increases with thecosine of the liquid-fiber contact angle (reaching a maximum where theangle is zero), and decreases with narrower capillary radii so thatnarrower capillaries will draw liquid from wider ones.

The relative wickability between facing layer 16 and the body of batt 14is affected by both the relative densities of the layers and therelative wettability of the individual fibers in each layer. The facinglayer is some times more dense than the body of the batt, tending toprovide greater wickability in the facing layer, but even then theindividual fibers of the batt have substantially smaller liquid-fibercontact angles than those of the facing layer, overcoming-the densitydifference and providing a substantial overall increase in capillarypressure to absorb liquid into the body of the batt,

Densified fiber layer 18 of the batt provides the maximum capillarypressure because it combines the very low contact angle of the fibers ofthe batt with the high density (small capillary radius) of the densifiedfibers.

When urine is voided into an area in facing layer 16, it partially wetsthe facing layer and is absorbed therein, spreading out to a limitedextent to form a roughly circular wetted zone therein. When the urinepasses through the facing layer and comes into contact with the body ofbatt 14, it is preferentially absorbed into the body of the batt becauseof the enhanced wettability thereof. It spreads within the body of thebatt to wet a roughly circular zone therein that is larger than thewetted zone in the facing layer. When the urine passes through the bodyof the batt into contact with densified layer 18, it is strongly drawntherein because of its high density and is spread laterally through amuch larger substantially circular zone, or to the edges of the batt,depending on the amount of urine passed.

On occasions when a substantial amount of urine has been voided, thedensified layer becomes saturated and excess urine, aided by thepresence of impervious sheet 12 and its adherence to the densified layerin a discontinuous pattern substantially throughout the interfacetherebetween, flows into the previously dry portions of the body of thebatt, and finally into the previously dry portions of the facing layer.It is to be noted, however, that such flow from a saturated densifiedlayer is from the outermost portions of the diaper inward so that mostof the facing layer remains dry until all other fibrous portions of thediaper are saturated. Furthermore, the marginal side and end portions ofthe facing layer are not readily wettable, and hence urine that doesflow back into the facing layer flows initially into the central portionto minimize the possibility of fluid leakage at the sides of the diaper.

The densified layer of the batt, for the reasons explained above,creates a high capillary pressure which tends to move liquid awayrapidly from the area of the original wetting. However, the speed ofliquid migra tion is limited in the densified layer because of theresistance provided by its small capillaries. The composite batt used inthis invention, with its densified layer in intimate contact withabsorbent material of lesser density, provides improved speed of liquidmigration over either the densified layer alone, or the uncompressedlayer alone.

While it is not desired to be bound by any particular theory ofoperation, it is believed that the improvement in speed of liquidmigration obtained by the cooperation of the dense and uncompressedlayers of the batts used in this invention results from the proximity ofthe two layers and the fact that just adjacent to the high capillarypressure generated by the dense layer are the large capillaries of theuncompressed layer which can move larger quantities of the liquid withrelatively little flow resistance.

There is also cooperation between the densified layer of the batt andimpervious sheet 12 to which it is adhered. A voiding of urine usuallytakes place within a short time, and the rate of absorption of thediaper might be overwhelmed during this short period in spite of thediaper's ultimate capacity to absorb the amount of liquid voided and inspite of the relatively high rate of absorption obtainable for thereasons specified above. The impervious sheet serves to hold the urineand keep it from wetting the bed clothes or outer clothing so that theabsorptive portions of the diaper can have the time to function. Inaddition, the impervious sheet serves as an anchor to stabilize thefluff portion of the batt against migration of the loosely compactedfibers, since the impervious sheet is adhered to the densified layerintegral with the fluff portion of the batt, over a widely distributedarea.

It is to be noted that the facing layer as assembled into the diaper iscoterminous with the impervious sheet and there is no folding over ofthe impervious sheet to envelope any edge of fibrous material. Thus,there is no portion of the upper surface of the diaper which is coveredwith any plastic material, and no plastic material comes into directcontact with the infant's skin when the diaper is affixed in position bypins or tabs. Prolonged direct contact of plastic material with aninfants skin can cause irritation and infection but, nonetheless, isemployed in prior art disposable diapers to provide an impervious sealto the infants skin. The superior absorptive capcity of the diaper ofthis invention and its superior functioning make such plastic-toskincontact unnecessary.

The diaper of this invention is normally packaged and sold in a foldedcondition. Briefly, the side margins 12b and 16b of the impervious sheet12 and the facing web 16, together with a portion of batt 14, are foldedinwardly in a first fold to provide as the uppermost layer of the fold,a portion of the moisture-impervious sheet. This sub-assembly is thenfolded outwardly along each edge in a second fold to cover the firstfolded portion and to expose the water-repellent edge portion of thefacing web as the upper layer of the double fold. In the preferredembodiment, each double fold at the edge of the diaper comprisesapproximately one-third of the resulting transverse dimension of thefolded diaper, leaving approximately one-third of the width of thefolded diaper as a central unfolded and uncovered portion.

The diaper is held in its folded condition by two small central spots ofadhesive applied between the main body of the diaper and the overlyingsides 16b of the facing web, one spot on each folded side of the diaper.When the diaper is to be put on the infant, the folds are opened on oneside of each of the adhesive spots, and the open portion of the diaperis put under the infants buttocks while the folded portion is raisedinto the crotch region. The final form of the diaper is shown inperspective on a reduced scale in FIG. 3.

In one form of the invention, as illustrated in FIG. 3, the diaper isprovided with adhesive tabs 26, each having a fixed end secured to theimpervious sheet 12 and a free end wherein the adhesive surface iscovered with a facing sheet. The facing sheets are removed to expose theadhesive surfaces when the diaper is applied to the infant, as in theconfiguration shown in FIG. 3, and the free ends of the adhesive tabsare secured to opposite corners of the diaper.

In the embodiment discussed above, densified layer 18 is a continuouslayer covering one entire face of batt 14. However, the densified layermay, if desired, be a widely distributed discontinuous layer, such as inthe form of parallel, narrow densified strips running lengthwise of thediaper and separated by narrow undensified trips. Alternatively, thedensified layer may be in the form of a rectangular grillwork ofdensified material encompassing a plurality of small areas ofundensified material. Densified layers of this latter type are made inthe same manner as the continuous densified layers described above,except that the compression is applied by embossed rollers, as describedin the aforementioned U.S. Pat. No. 3,017,304.

Suitable fibrous structures for making the pads or batts 14 used in thisinvention are made from short cellulosic fibers obtained by the grindingor comminution of compacted wood pulp fibers or cotton linters. Thecompacted cellulosic material is at a moisture content of 5-10 weightpercent before being subjected to the grinding operation so that thefibers produced by grinding have sufficient moisture to have thecapability of developing weak interfiber hydrogen bonds which give somecoherenee to the body of the batt.

The batts are initially formed by air blowing the slightly moistcellulosic fibers onto a support at a total weight of about 2 to about10 oz./yd and then subjecting the air blown fibers to heavy comprssion.

The dense compacted paper-like layer or skin is prepared by moistening asurface of the cellulosic batt with a fine spray of water, and thensubjecting the moistened batt to pressure. The formation of thedensified skin on the cellulosic batt is believed to be due to theformation of strong hydrogen bonds between contacting moistened fibers,similar to the bonds between the fibers in paper. By the properselection of the amount of moisture applied to the surface of the battand by the proper selection of degree of compression imposed, theproperties of the densified skin may be varied as desired. Thethickness, density, strength and other characteristics of the densifiedskin will depend upon the uniformity by which the moisture is applied,the depth to which it penetrates, and the degree to which the fibers arecompressed. For example, by finely spraying about 0.0015 cc of H O/cm.of web surface and then exposing the web to a pressure of about 40lbs./in.", a suitable densified, coherent paperlike skin 18 is obtainedon the surface of the web which has been moistened.

The short fibers used in making batts 14 of this invention are generallyentirely fibers of wood pulp or cotton linters. However, othercellulosic fibers may be used as well as blends of cellulose fibers withother fibers such as silk, wool, nylon and cellulose acetate. Highlypurified kraft paper pulp fibers have proven to be most satisfactory formost applications.

The diaper of this invention may be assembled in equipment such as thatschematically shown in FIGS. 4, 5, 6 and 7, FIGS. 5 and 6 beingparticularly relevant to the diaper of FIG. 1 and FIG. 7 beingparticularly relevant to the diaper of FIG. 8. As shown in FIG. 4, aroll of compacted wood pulp 41 is provided to feed a source of shortcellulosic fibers to grinding mill 42 from which a stream of fibers isblown onto belt 43 as a layer 44 weighing between about 2 and about 10oz./yd'.

Mill 42 grinds the pulpboard into individual short fibers. However, inone preferred embodiment, some of the pulpboard fibers are notcompletely comminuted and remain joined to other fibers in small clumps,generally smaller than about 54 inch across. It has been found that thepresence of such small clumps of fibers in the body of batt 14 providesislands of increased tenacity for holding liquid. When an infants weighton one portion of the batt densifies that portion and tends toconcentrate the liquid in the densified portion, the presence of clumpsof fibers elsewhere in the batt tends to hold the liquid in place.Preferably from about 2 to about 10 weight percent of the fibers shouldbe in the form of such clumps.

The air blown layer is passed under compacting roll 46 from which itemerges with enough integrity to sustain itself as a web without thesupport of belt 43. The web then passes through a pair of calender rolls47 for further compression and then under nozzle 48 which deposits afine spray of'moisture on the upper surface of the web. The moistenedweb then passes between another set of calender rolls 49 which exertheavy pressure on it to form a skin 51 on its upper surface.

The amount of moisture applied to the web may vary suitably from about0.0005 to about 0.03 cc. of H O/cm. of web surface, depending on thethickness of the web and the thickness of the paper-like densified skindesired, with lesser amounts of moisture being used for thinner webs andvery thin, papery skins and greater amounts for thicker webs and skinsof greater thickness.

The amount of pressure applied by rolls 49 may vary from about 5 toabout 100 or more 1bs./in. with the commercially preferable range beingfrom about 10 to about 50 lbs/in? In a typical embodiment, the web issprayed with about 0.0015 cc. of H O/cmf" of web surface and subjectedto a pressure of about 40 lbs/in. to obtain a densified, coherent paperyskin on the surface of the web which has been moistened.

In the absorbent web and in the batts cut therefrom, there are weakhydrogen bonds in the body of the batt providing sufficient strength tomaintain the integrity of the batt in ordinary handling, and there arestrong hydrogen bonds in the densified layer or skin to increase thecohesive strength of the composite. After the skin is formed, theabsorbent web comes into contact with a web of facing material 52 and issupported thereby while being cut by cutter 53 into individual batts 14.

The facing material is prepared by initially feeding a source 54 ofshort fibers and a source 55 of long fibers to a fiber individualizingand mixing means 56, which removes the fibers from their respectivesources, mixes them, and deposits them on a foraminous belt 57. The webforming means maybe similar to a Rando-Webber made by the Curlator Co.To produce the diaper of FIG. 1, the web is then moved by belt 57beneath weir boxes 58 and 59 which apply binder material to the web, ascan be best seen in FIG. 5.

The facing layer, as described above, contains between percent and 98percent by weight of short fibers, not exceeding about $4" in length.The average short fibers are from about 1/16 to about 3/16 inch inlength. The web of randomly laid dry fibers of the desired mix of shortand long lengths has a density from about 0.09 gm./cc. to about 0.025gm./cc. measured by ASTM Method D1777 at 0.16 lbs.in.

Facing layers having weights between about 1 and about 5 oz./yd.preferably 1 to 2 oz./yd. are generally suitable for use in thisinvention. One particular facing layer which has been used withsatisfaction is composed of approximately 15 percent textile lengthfibers such as uniformly cut 1% inch 1.5 denier rayon fibers and percentfibers of individualized second cut cotton linters. This facing layerhas a weight of about 2 oz./yd. A bonding agent, such as aself-crosslinking acrylic emulsion, is applied to the web to retain thefibers in their assembled relationship. One bonding agent which has beenemployed with considerable success is a latex of a polyethyl-acrylatecopolymer containing small amounts of acrylonitrile and a crosslinkingmonomer sold under the trademark HYCAR 2600 X 120. The bonding agentshould preferably be of the low viscosity type with a viscosity lessthan 5 centipoises.

The downstream weir box 58 is designed to apply binder material to onlythe marginal side edges of the web, and hence a barrier 60 is providedcentrally of the weir box, so that binder material can fiow outwardlyonly through the openings 61 at the sides of the weir box. The bindermaterial may be of the acrylic latex type, as described above, and asufficient quantity is flowed onto the web to completely impregnate thesame throughout the thickness of the marginal edges.

The web then passes to the downstream weir box 59, which includesinwardly extending barriers 62 at opposite sides thereof which areessentially aligned with openings 61, so that binder material withinweir box 59 flows outwardly through the central opening 63 betweenbarriers 62 and impregnates the central or midportion of the web.

The binder material which is fed to weir box 59 includes a wettingagent, such as an anionic or non-ionic surfactant, and sufficientquantities of binder and wetting agent are applied to the centralportion of the web to thoroughly and completely impregnate the same.Typical surfactants which have been found to be suitable are the anionicsulfonated alkyl ester sold under the trademark Triton GR-S and thenon-ionic polyoxyethylene sorbitan monolaurate sold under the trademarkTWEEN 20. The binder material that is fed to the weir box 58 does notcontain a wetting agent, so that the edge portions 160 of the facinglayer are given the desired water repellent characteristics. By way ofexample, the edge portions 16a may each extend inwardly 1 inch in apanel that is 11 inches wide.

The composition of the binder suspension is controlled in a typicalapplication so as to give the fabric a dry solids add on of 6 percentbased on the fabric weight, of which about 0.15 percent is the amount ofsurfactant. A suitable range for the amount of binder is from about 4%percent to about 9 percent, based on fabric weight.

An alternative form of binder applying means is illustrated in FIG. 6,and with the arrangement illustrated therein, a pair of side-by-sidefacing layers can be simultaneously bonded. A web of substantiallydouble width is initially fed past a downstream weir box 64 whichincludes spaced barriers 65 and 66 that define slots 67 and 68 inalignment with the side edges of the web, and that also defines anopening 69 that is disposed centrally of the web. Opening 69 isapproximately twice as wide as openings 67 and 68, which are of equalwidth. The binder that is fed to weir box 64 is the same as the bindermaterial that is fed to weir box 58, i.e., the binder does not contain awetting agent.

After the web passes from beneath weir box 64, it moves beneath afurther weir box 70 that includes relatively narrow projections 71 and72 at opposite sides thereof, and a relatively wide projection 73 at themidportion thereof. Projections 71, 72 and 73 correspond in width toopenings 67, 68 and 69, respectively. The binder material that is fed toweir box 70 is the same as that fed to weir box 59, Le, the bindermaterial has a wetting agent therein. As with the embodiment of FIG. 5,when the web emerges from beneath weir box 70, relatively narrow waterrepellent strips 160 are provided at opposite sides of the web. Arelatively wide strip 160 is provided centrally of the web, with strip160 being substantially twice the width of strips 16a. The web thenpasses beneath a centrally disposed cutter 74 that severs the web intotwo separate facing layers 16.

With either of the above arrangements, the binder fluid is flowed ontoand through the web in quantities substantially in excess of theultimate amount to be deposited on the fibers completely impregnatingthe web.

The web, immediately after impregnation with the binder fluid, passesover a suction box 75 where excess binder fluid is removed. The wet webis then conveyed into a drying oven 76 having a temperature of310-320F., where it is dried and the resin binder cured. The resultantmaterial has a density of 0.05 to 0.07 gm./cc., and a dry strength ofabout 1.4 lbs/in. of width in the cross direction. The wet strengths areabout 0.9 lbs/in. of width in the machine direction and about 0.5lbs/in. of width in the cross direction. The fabric may then becollected on a storage roll, or rolls, now shown, or pass directly tothe batt material, as shown in FIG. 4.

Polyethylene film 12 is fed to the assembly from roll 77, lines ofadhesive being applied from applicator 78. As described above, theadhesive is applied as parallel lines or beads between the impervioussheet and the densified layer of the batt (or the facing layer in themarginal portion of the diaper). Adhesive may, if desired, be applied asa continuous layer between the polyethylene and the batt, but suchapplication tends to provide excessive stiffness. The adhesive may alsobe applied in other patterns, such as spaced dots or other forms ofso-called island bonds, but fairly close overall adhesion between thesheet and the batt is required and no portion of the polyethylene shouldbe more than about 2 inches from a point of adhesion. In the absence ofsuch close overall adhesion, the polyethylene film may be separated fromthe densified layer to create substantial spaces in which uncontrollablylarge amounts of free liquid urine can accumulate.

After the facing material and polyethylene are brought into contact withopposite faces of the absorbent batts, the assembly is subjected tocompression by rolls 79 and 80 to shape the diaper assembly, and theindividual diapers are cut off by cutter 81.

If desired, adhesive applicator 78 may be omitted and adhesion betweenthe polyethylene layer and the fibrous layers may be achieved by heatsealing, employing a suitable sealing element in the production line.

If desired, the facing layer may be made with a veneer of long fibers onone or both surfaces thereof, in place of or in addition to the longfibers intermixed with the short fibers. In another embodiment, thefacing layer may be made substantially entirely of textile length fibersbonded together with a resinous bonding agent. This embodiment canprovide a facing layer of greater strength, but it is not preferredbecause it is more expensive and because the strength of the short fibercontaining facing material is adequate in most instances.

The adherence of the impervious layer to the densified layer,continuously or discontinuously. over substantially the entire interfacebetween them is important because it prevents substantial separationbetween the two and the creation of substantial spaces in whichsubstantial amounts of free liquid urine can accumulate. The adherenceof the impervious layer to the paper-like densified cellulosic layereffects a dimensional stabilization of the densified layer againsttransverse movement and thereby brings about a stabilization of theloosely compacted fiber fluff portion of the batt layer since thepaper-like densified layer is integral with the fluff portion of thebatt, and holding forces are transmitted from the dimensionally stableimpervious layer through the widely distributed adhesive, to thedensified layer, and thence to the fluff.

The binder application system of FIG. can also be used when it isdesired to make a diaper witha facing layer having areas of lesserwettability in the end margins rather than in the side margins. In thisinstance, the facing web width is of sufficient dimension to comprisethe length of the facing layer on the diaper of FIG. 1 and the web,after drying, is cut into diaper widths for assembly with the remainingdiaper elements.

When it is desired to have areas of lesser wettability at both the sideedges and the end edges, the system of FIG. 7 may be substituted for thesystem of FIG. 5 as the binder application system within the overallassembly system of FIG. 5.

The FIG. 7 system includes two spaced apart through printing assemblies150 and 170. Assembly 150 is designed to through print a mixture ofbinder and surfactant onto the central area portion of web 116 toprovide rectangular area 116a which has the desired wettability for theportions of the facing layer through which urine must pass. To this end,roller 151 is provided which rotates in the direction of the web feed(downward and to the left as shown in FIG. 7). Roller 151 is hollow andcontains a small quantity of the desired binder-surfactant mixture,maintained at a low level therein by continuous supply through line 156.The cylindrical surface of roller comprises solid areas 152 and 153corresponding respectively to the side and end margins of lesserwettability desired in the facing layer and perforated areas 154corresponding to the rectangular area 116C on the web. Suction box 157is below the web where it is in contact with roller 151 and helps pullthe binder-surfactant mixture through the perforations in area 154 andthrough the web when the perforations are under the shallow pool ofliquid and over the web. As the web emerges from under roller 151 it iswet with the binder-surfactant mixture in the areas 116c and dry in theareas 116a and 116d.

Roller 171 in assembly 170 serves to apply binder without surfactant tothe areas left dry by roller 151. Roller 171 is also hollow and containsa shallow pool of a binder composition provided by line 176. Thecylindrical surface of roller 171 is the complement of the cylindricalsurface of roller 151 in that the latter is solid in area 174corresponding to area 116C on the web and is perforated in areas 172 and173 corresponding to the side and end margins of the facing layer.

The rotating roller 171 cooperates with suction box 177 to wet thepreviously unwetted portions of the web with the water repellent bindersolution to produce, after drying and cutting, the desired marginalareas 116a and 116d of FIG. 8 having lesser wettability than theremainder of the facing layer.

In the modification described above, the desired water repellency isapplied to the marginal portions of the facing web in strips extendingfrom the more wettable central area to the edges of the web. In analternate embodiment, the water-repellent marginal portion of the facinglayer may be narrower strips forming a a barrier to outward flow ofliquid from the more wettable centralarea but not extending as far asthe edge of thev facing layer.

Facing layer 116 in FIG. 8 extends beyond the edges of batt 114, as inFIGS. 1 and 9, and strips 116a and 116d in the side and marginal area,respectively, of the facing layer between the edges of the batt and theedges of the facing layer, but spaced from both, serve as dams toprevent the flow of liquid outwardly from the more wettable central areato the edges of the diaper. If desired, the facing layer need not haveboth strips 116a and 116d and may instead have either side strips or endstrips depending on the particular design of the diaper and the relativelikelihood of leakage through the sides or through the ends of thediaper.

Strips 116a and 116d should be of sufficient width to serve as aneffective barrier to the easy transmission of aqueous fluids, thenecessary width being inversely related to the degree of unwettabilityin the strip. Generally, strips 116a and 116d range in width from abouta to about 11 inches.

It will be understood by those skilled in the art that variations andmodifications of the specific embodiments described above may beemployed. For example, while facing layer 16 has been described indetail as having utility in a disposable diaper, it may also be used insimilar products intended to absorb body fluids, such as a bed pad.

It should also be understood that the invention is applicable to otherforms of facing layers and other forms of absorbent pads having greaterwettability than the facing layers.

Among the alternative facing layers which may be utilized in accordancewith this invention and provided with marginal areas of lesserwettability are porous, paper-like facing materials made of long fibersbonded together with a thermoplastic binder applied in emulsion form,such as the facing layers disclosed in Duncan et al US. Pat. No.3,180,335, issued Apr. 27, 1965, and open-celled polymeric foam facings,such as those disclosed in Maisel, et al., US. Pat. No. 3,431,911.

Among the alternative absorbent pads which may be used in accordancewith this invention are pads made of a plurality of plies of cellulosewadding, as disclosed in the aforementioned Duncan, et al, patent.

Other modifications and variations will be apparent to those skilled inthe art.

I claim:

1. A multi-layer diapercomprising: a backing layer; a highly absorbentpad disposed in face-to-face juxtaposition to said backing layer; and afacing layer on the side of said pad opposite said backing layer; saidfacing layer comprising a through bonded non-woven fabric of mixed shortand long fibers, said fabric having a short fiber content of at leastabout percent by weight of the fabric, said short fibers having a lengthless than 5 1 inch and said long fibers having a length greater than 11inch, said fibers being bonded by a cross-linked binder appliedthrough-out the thickness of said fabric in an amount between about 1percent and about 30 percent of the weight of the fibers on a dry solidsbasis, said fabric having a weight of less than 8 oz./yd. and a densityof 0.05 to 0.15 gm./cc., said fabric being treated with a rewettingagent to give it a desired degree of wettability for water, the ratio ofsaid binder to said rewetting agent in the mid-portion of said fabricand in the marginal portions at least at the sides thereof being variedso that said marginal portions have less absorbency and less wettabilityfor water than the mid-portion of said fabric.

2. The diaper of claim 1 wherein said facing layer and said backinglayer are rectangular and substantially coextensive, said pad issubstantially rectangular, narrower than said facing layer and saidbacking layer and centrally disposed with respect thereto to providemarginal portions of said diaper in which said facing layer and saidbacking layer are in direct contact with each other.

3. The diaper of claim 2 wherein said marginal portions of lesswettability for water than said mid-portion extend in width from saidmid-portion to the side edges of said fabric.

4. The diaper of claim 2 wherein said mid-portion of said facing layeris wider than said pad, and said marginal portions are narrow, extendingin width from the sides of said mid-portion to lines spaced inwardlyfrom the side edges of said fabric.

5. The diaper of claim 2 wherein said marginal portions of said facinglayer and said backing layer are adhered to one another.

6. The diaper of claim 1 in which the short and long fibers of saidfacing layer are randomly dispersed and uniformly distributed.

7. The diaper of claim 1 in which the short and long fibers of saidfacing layer are in different proportions in different thicknessportions of said diaper with the outermost face of said facing layerhaving a greater proportion of long fibers than the overall proportionof long fibers in the entire facing layer.

8. The diaper of claim 1 wherein said marginal side edges contain alesser amount of rewetting agent than said mid-portion.

9. The diaper of claim 1 wherein said marginal side edges contain agreater amount of binder than said midportion.

10. A multi-layer diaper comprising: a porous facing layer in the formof a water-wettable web of mixed long and short fibers, said web beingthrough bonded with a cross-linked binder and treated with a rewettingagent to give it a desired degree of wettability for water, the ratio ofsaid binder to said rewetting agent in the midportion of said web and inthe marginal side and end portions thereof being varied so that saidmarginal portions have less absorbency and less wettability for waterthan the mid-portion of said web; a highly porous, loosely compacted,cellulosic fibrous batt in face-toface juxtaposition to said facinglayer and having greater wettability to water than said facing layer; apaperlike, densified compacted cellulosic fibrous layer of relativelyhigh wettability and relatively high fluid retentivity integral withsaid loosely compacted batt on the face thereof opposite the face injuxtaposition to said facing layer; and a water-impervious backing sheetadhered to said densified layer.

11. The diaper of claim 10 wherein said backing sheet and said facinglayer are substantially rectangular and substantially coextensive, saidbatt is substantially rectangular, narrower than said backing sheet andfacing layer, and centrally disposed with respect thereto to providemarginal portions of said diaper in which said backing sheet and saidfacing web are in direct contact with each other.

12. The diaper of claim 10 wherein the fiber content of said facinglayer comprises from about to about 98 weight percent of short fibershaving a fiber length less than 5 1 inch and from about 2 to about 25weight percent of long fibers having a fiber length between about V2 and2%.

13. The diaper of claim 10 wherein said side and end marginal portionsextend in width from said midportion to the side and end edges of saidfacing layer.

14. The diaper of claim 10 wherein said mid-portion of said facing layeris wider and longer than said batt, and said marginal portions arenarrower, extending in width from the sides and ends of said mid-portionto lines spaced inwardly from the side and end edges of said fabric.

15. The diaper of claim 10 wherein said central portion comprises fromabout 50 percent to about percent of the area of said facing layer.

16. The diaper of claim 10 wherein said marginal portions include sidemarginal portions and end marginal portions and are from about inch toabout 2 inches in width.

17. The diaper of claim 10 wherein said marginal portions include sidemarginal portions and end marginal portions and are spaced inwardly fromthe side

2. The diaper of claim 1 wherein said facing layer and said backinglayer are rectangular and substantially coextensive, said pad issubstantially rectangular, narrower than said facing layer and saidbacking layer and centrally disposed with respect thereto to providemarginal portions of said diaper in which said facing layer and saidbacking layer are in direct contact with each other.
 3. The diaper ofclaim 2 wherein said marginal portions of less wettability for waterthan said mid-portion extend in width from said mid-portion to thE sideedges of said fabric.
 4. The diaper of claim 2 wherein said mid-portionof said facing layer is wider than said pad, and said marginal portionsare narrow, extending in width from the sides of said mid-portion tolines spaced inwardly from the side edges of said fabric.
 5. The diaperof claim 2 wherein said marginal portions of said facing layer and saidbacking layer are adhered to one another.
 6. The diaper of claim 1 inwhich the short and long fibers of said facing layer are randomlydispersed and uniformly distributed.
 7. The diaper of claim 1 in whichthe short and long fibers of said facing layer are in differentproportions in different thickness portions of said diaper with theoutermost face of said facing layer having a greater proportion of longfibers than the overall proportion of long fibers in the entire facinglayer.
 8. The diaper of claim 1 wherein said marginal side edges containa lesser amount of rewetting agent than said mid-portion.
 9. The diaperof claim 1 wherein said marginal side edges contain a greater amount ofbinder than said midportion.
 10. A multi-layer diaper comprising: aporous facing layer in the form of a water-wettable web of mixed longand short fibers, said web being through bonded with a cross-linkedbinder and treated with a rewetting agent to give it a desired degree ofwettability for water, the ratio of said binder to said rewetting agentin the mid-portion of said web and in the marginal side and end portionsthereof being varied so that said marginal portions have less absorbencyand less wettability for water than the mid-portion of said web; ahighly porous, loosely compacted, cellulosic fibrous batt inface-to-face juxtaposition to said facing layer and having greaterwettability to water than said facing layer; a paperlike, densifiedcompacted cellulosic fibrous layer of relatively high wettability andrelatively high fluid retentivity integral with said loosely compactedbatt on the face thereof opposite the face in juxtaposition to saidfacing layer; and a water-impervious backing sheet adhered to saiddensified layer.
 11. The diaper of claim 10 wherein said backing sheetand said facing layer are substantially rectangular and substantiallycoextensive, said batt is substantially rectangular, narrower than saidbacking sheet and facing layer, and centrally disposed with respectthereto to provide marginal portions of said diaper in which saidbacking sheet and said facing web are in direct contact with each other.12. The diaper of claim 10 wherein the fiber content of said facinglayer comprises from about 75 to about 98 weight percent of short fibershaving a fiber length less than 1/4 inch and from about 2 to about 25weight percent of long fibers having a fiber length between about 1/2and 2 1/2 .
 13. The diaper of claim 10 wherein said side and endmarginal portions extend in width from said mid-portion to the side andend edges of said facing layer.
 14. The diaper of claim 10 wherein saidmid-portion of said facing layer is wider and longer than said batt, andsaid marginal portions are narrower, extending in width from the sidesand ends of said mid-portion to lines spaced inwardly from the side andend edges of said fabric.
 15. The diaper of claim 10 wherein saidcentral portion comprises from about 50 percent to about 90 percent ofthe area of said facing layer.
 16. The diaper of claim 10 wherein saidmarginal portions include side marginal portions and end marginalportions and are from about 1/2 inch to about 2 inches in width.
 17. Thediaper of claim 10 wherein said marginal portions include side marginalportions and end marginal portions and are spaced inwardly from the sideand end edges.